A power semiconductor device to supply power to a load is known. The power semiconductor device called an intelligent power device (IPD) is used in an electronic control system of a car to control supply of power to a headlight and so on according to an instruction from a microcomputer. In such a power semiconductor device, generally, a high side switch is used (For example, Patent Literature 1).
FIG. 1 shows a configuration of the power semiconductor device described to Patent Literature 1. The power semiconductor device has a power supply terminal TV, an output terminal TO, an output transistor 210, a control circuit 220, a resistance 230, a discharge transistor 240 and a zener diode 250. A power supply voltage VCC is supplied to the power supply terminal TV.
The output transistor 210 is connected between the power supply terminal TV and the output terminal TO. In detail, the output transistor 210 is an N-channel MOSFET, and its gate, drain and source are connected with a node N1, the power supply terminal TV and the output terminal TO, respectively. The output terminal TO is connected with one end of a load and the other end of the load is connected with a ground terminal. Thus, the output transistor 10 is connected to function as a high side switch.
The resistance 230 is connected between the node N1 and the output terminal TO. The discharge transistor 240 is an N-channel MOSFET, and its gate, back gate, drain and source are connected with a node NB, a node NC, the node N1 and a node N2, respectively. The node NC (back gate) and the node N2 (source) are short-circuited. An anode and cathode of the zener diode 250 are connected with the node N2 and the ground terminal TG, respectively. The route from the node N1 to the ground terminal TG through the discharge transistor 240 and the zener diode 250 is a discharge route for the node N1.
The control circuit 220 controls the charging and discharging operations of the node N1 connected with the gate of the output transistor 210. In detail, in case of power-on, the control circuit 220 sets a voltage of the node NB to a low level so as to turn off the discharge transistor 240. Thus, the discharge route which goes through the discharge transistor 240 is deactivated. On the other hand, the control circuit 220 charges the node N1 to turn on the output transistor 210. Thus, the power is supplied to the load connected with the output terminal TO.
In case of power-off, the control circuit 220 stops the charging to the node N1. Also, the control circuit 220 sets a voltage of the node NB to a high level, to turn on the discharge transistor 240. Thus, a current flows from the node N1 to the ground terminal TG through the discharge transistor 240 and the zener diode 250, so as to discharge from the node N1. At the same time, a current flows from the node N1 to the output terminal TO through the resistance 230 so as to discharge from the node N1. Therefore, the node N1 is discharged rapidly and the voltage at the node N1 reduces rapidly. As a result, the output transistor 210 is turned off quickly.